The drives for walking beam transfer devices most often consist of two separate drive units. The first is a lift drive; it normally is a parallel plate cam-type oscillator drive unit with a crank arm and link connecting the drive to the transfer beam to be lifted. The second is a horizontal slide drive; it usually comprises a parallel-plate-cam-type index drive unit which also has a crank arm and link connecting it to the transfer beam to be horizontally slid.
Both such lift and horizontal slide drives normally require separate drive motors, gear reducers, overload clutches, and electrical sensing devices to maintain timing of one drive unit with the other. Further, only relatively short transfer strokes, i.e., horizontal slide motions, of approximately 10-15" maximum in length are available with the walking beam drives presently available. Longer horizontal strokes are available only with the addition of relatively expensive hypo-cycloidal arms.
The present invention provides a novel walking beam drive apparatus utilizing a single drive unit having two internal cams. These two drive cams are keyed to a common shaft in the single drive unit so that timing between the lift and rotation motions is constant and cannot be lost as would be the case with the dual drives of the prior art. One of the two cams provides a lifting motion to an output dial mounting plate while the other provides a rotary motion to that plate; the rotary motion is then converted into linear sliding motion.
A lift carriage assembly is guided for vertical movement upon stationary vertical guide posts having linear bearings. This lift carriage assembly is attached to the output dial mounting plate of the cam-actuated drive unit by means of a large diameter bearing which allows rotary motion of the output dial mounting plate without rotating the lift carriage assembly, the latter being stabilized against rotation by the vertical guide posts upon which it rides. However, as the output dial mounting plate of the cam-actuated drive is vertically raised and lowered, so is the lift carriage assembly correspondingly raised and lowered.
A horizontal slide carriage assembly is slidingly supported on the lift carriage assembly by use of horizontal guide rods and linear bearings. A crank arm with roller follower is mounted to a raised hub of the output dial mounting plate. The crank arm's roller rides within a Scotch yoke-type track mounted to a mounting plate of the horizontal slide assembly. In this fashion, the rotary motion of the output dial mounting plate is converted into horizontal sliding motion such that the horizontal slide assembly can be linearly moved relative to the lift carriage assembly.
Thus, it is a principal object of the present invention to provide a cam-actuated drive apparatus for a walking beam transfer device which drive apparatus has two drive cam members for providing one output member with both rotary motion and lifting motion, and structure for converting the rotary motion into horizontal sliding motion.
It is a further object of the present invention to convert a cam-actuated rotary pick-and-place drive unit into a walking beam drive apparatus.
It is a still further object of the present invention to utilize a cam-actuated single drive unit which provides both lifting and rotary motions for a walking beam drive apparatus without the need for any sensing mechanisms to correlate the timing of the respective lift and linear transfer drive motions.
It is another object of the present invention to provide a walking beam drive apparatus which has structure for supporting a lift carriage on a rotating and vertically oscillating output member of a rotary pick-and-place drive unit without effecting any rotation of the lift carriage, and also structure for converting the rotary output motion of the output member into linear sliding motion of a horizontal slide carriage which is slidingly supported on the lift carriage.